ML20151L709
| ML20151L709 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 07/31/1997 |
| From: | Ruland W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Sellman M Maine Yankee |
| Shared Package | |
| ML20151L714 | List: |
| References | |
| NUDOCS 9708070161 | |
| Download: ML20151L709 (40) | |
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July 31, 1997 Mr. Michael B. Sellman President Maine Yankee Atomic Power Company 329 Bath Road Brunswick, Maine 04011 l
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SUBJECT:
MAINE YANKEE CABLE SEPARATION
Dear Mr. Sellman:
On July 22,1997, members of your staff, including Mr. M. Meisner and Mr. L. Lozano, j
visited the Region 1 office to tell the NRC Staff the current approach taken on the cable separation project currently in progress at Maine Yankee. This open and announced meeting was attended by staff members from Region I and NRR, as well as members of the public.
The presentation included a brief history of cable separation at Maine Yankee from original construction to the present. An overview of the results of the present cable separation review project was presented, as well as future plans to modify the licensing basis using the 10 CFR 50.59 process.
i At the conclusion of the presentation, Mr. Meisner distributed copies of Maine Yankee's Technical Evaluation, TE 172-97, Cable Separation Safety Assessment Report, Rev. O, i
dated July 21,1997. The staff indicated that the acceptability of that safety assessment would be subject to review during a future inspection.
l Sincerely, ORIGINAL SIGNED BY:
William H. Ruland, Chief j
Electrical Engineering Branch
/
Division of Reactor Safety
/
Docket No:
50-309 License No:
DPR-36 f
Enclosures:
Mi
- 1. Maine Yankee Presentation, Overhood Slides j
- 2. Maine Yankee Cable Separation Safety Assessment Report
- 3. List of Attendees 9708070161 970731 PDR ADOCK 05000309 P
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8 Mr. M. Sellman 2
cc w/encis:
r G. Leitch, Vice President, Operations M. Meisner, Vice President, Licensing and Regulatory Compliance i
R. Fraser, Vice President, Engineering J. M. Bicck, Attorney at Law l
P. L'. Anderson, Project Manager (Yankee Atomic Electric Company)
R. Blackmore, Plant Manager L. Diehl, Manager of Public and Governmental Affairs J. A. Ritsher, Attorney (Ropes and Gray) 4 P. Dostie, State Nuclear Safety inspector P. Brann, Assistant Attorney General U. Vanags, State Nuclear Safety Advisor i
C. Brinkman, Combustion Engineering, Inc.
W. D. Meinert, Nuclear Engineer j
First Selectmen of Wiscasset Maine State Planning Officer - Nuclear Safety Advisor l
l State of Maine, SLO Designee State Planning Officer - Executive Department j
Frienes of the Coast j
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Mr. M. Sellman 3
Distribution w/encls:
Region i Docket Room (with concurrences)
Nuclear Safety information Center (NSIC)
PUBLIC NRC Resident inspector C Miskey, DRS Distribution w/o enci 2:
J. Wiggins, DRS W. Axelson, DRA H. Miller, RA C. Cowgill, DRP D. Bearde, DRP Distribution w/o encls 1 and 2 (VIA E-MAIL):
W. Dean, OEDO S. Varga, NRR D. Dorman, PM, NRR M. Callahan, OCA R. Correia, NRR C. Smith, NRR F. Talbot, NRR D. Thatcher, NRR N. Trehan, NRR D. Chawaga, ORA D. Screnci, PAO N. Sheehan, PAO G. Guthrie, DRP R. Summers, DRP inspection Program Branch, NRR (IPAS)
DOCDESK i
DOCUMENT NAME: A: MYCABLE. PRS t
To seceive a copy of this document. InJicate in the box: "C" u Copy without attachment /enclosurc
- E" = Copy arith attachment /enclosurc
'N" = No copy l
OFFICE Rl/DRS lc.
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NAME GMorris ffM WRutany'jffff CCowgillK.%/o l
DATE 07/25/97 74//97
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7/ 3l /97 l
OFFICIAL RECORD COPY i
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ENCLOSURE 1 Maine Yankee Resolution of Cable Separation issues July 22,1997 1
k Agenda l
l Introduction and overview Mike Meisner l
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Problem scope and root causes Lu Lozano
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Revised safety basis Lu Lozano Safety basis implementation Lu Lozano e
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Conclusions Mike Meisner 1
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Cable Separation issue Identification Discovered early December,1996 during Maine Yankee e
reviews associated with Generic Letter 96-01 (logic circuit testing) i identified discrepancies between field cable installation and e
the licensing basis (i.e., FSAR)
Led to formation of the Cable Separation Assessment &
e Walkdown Project to:
e Determine the extent of the condition Resolve discrepancies e
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Cable Separation Problem Scope Discrepancies due to cable installation associated with e
design changes implemented following plant startup Approximately 800 SR (safety related) and NNS (non-e nuclear safety) power cables i
Primarily related to post-TMI modifications e
inspections and root cause evaluation confirmed that i
e discrepancies didn't extend to original construction j
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No. of Cables Installed Por Refu:aling l
160 140 i
Q 120 i
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1 1972 1974 1975 1977 1978 1 80 198 1982 1984 198 19 1988 1990 1992 1993 1995 Year Note: Initial construction (1972)
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Approach to Resolution r
Understand the past Develop a safety basis for the future
~ Apply the safety basis to all plant cables
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l Understand the Past i
Confirm problem scope through detailed inspections e
Design changes vs. original construction e
Extent of condition Determine root cause(s) of the discrepancies l
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Develop a Safety Basis for the Future 4
Recognize that:
e Original cable spearation/ independence licensing basis
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e (circa 1968) lacked technical rigor i
4 Industry Standards and criteria for cable separation had e
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not yet been developed h
Restoration to original license basis in some cases e
would provide little safety improvement We have a better understanding today of the circuit e
4 independence elements important to safety Take a technically sound approach, focused on safety, in e
l moving forward Identify the hazards which could adversely affect cable e
performance Understand the safety benefits associated with cable e
separation / independence Either eliminate the hazard or ensure adequate circuit independence Modify design / licensing bases as necessary to implement a e
new safety basis 9
i
I implement the New Safety Basis for Circuit Independence Resolve discrepancies (apply to all cables - not just the e
problem scope cables) l e
Restore to design basis e
Repull/ reroute cables Install appropriate metal barriers l
e Provide protection against external hazards e
Accept "as found" configuration based on an altemate e
method of achieving independence (e.g., install l
overcurrent interruption devices; eliminate hazards)
Modify design / license basis as necessary under e
10CFR50.59 Complete root cause corrective actions (e.g., tray labeling, e
l program / procedure upgrades, drawing upgrades, etc.)
4 10 l
l' Additional Information i
i Cable separation assessments and resolution overseen by an expert panel i
Expertise in cable separation issues (e.g. past IEEE e
l code committee chairmen) and licensing bases of l
plants of similar vintage i
l Members independent from Maine Yankee, with one exception l
Current cable separation issues are distinct from those raised by Atherton memo i
Atherton focused on fire protection issues, largely e
resolved through Altemate Safe Shutdown System (Appendix R compliance)
Current issues are associated with design changes that e
occurred after Atherton's inspection l
11
Cable Separation Problem Scope and Root Causes i
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l Assessment /Walkdown Scope e
in excess of 100,000 man-hours included all of the 800 SR (all types) and NNS (power only) e l
cables associated with design changes e
included a significant number of original construction cables (in excess of 1200 cables and 27,000 cable transitions) l l
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l Assessment Findings Original vs. New Construction e
inspection resuits confirm:
Loss of control over cable separation installation e
requirements after original construction Consistent application of cable separation criteria during original construction
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Discrepancies requiring action:
e Original construction: 5 (
1%)- no commonalities New construction: Approximately 120 (15% of post-e construction cables - some discrepancies apply to more than one cable)- common root cause 1
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Root Cause Cable separation criteria established during original l
o construction were not compiled into a design basis summary document and, therefore, not consistently applied to design changes after construction e
Contributing to the root cause:
Ambiguous and conflicting cable separation criteria, inaccurate drawings and less than adequate cable and i
tray labeling The design change process lacked relevant self-e assessment activities to identify and resolve such problems The corrective action program and the quality e
assurance organization focused on self-disclosing problems with too high a threshold for formal evaluation, or did not fol!ow up on identified problems Training for engineers and craft responsible for e
implementing cable separation requirements was less than adequate 15
Walkdown Summary of Discrepancies Cable in the wrong raceway o
Cables cross at cable tray tee e
No barrier or degraded barrier irl tray Cable tray overfilled -
e Control cable run with instrument cable No barrier or required air space at transition e
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Power cable run with control cable Power cable near instrument cable t
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i' Redirection in Assessment Approach i
Walkdowns demonstrated that all unique types of e
discrepancies had been identified (prehus overhead) i Evaluation of walkdown findings were incomplete, in that all e
instances of discrepancies had not yet been identified e
Walkdowns demonstrated that:
The solution to the discrepant conditions would require e
development of a new safety basis for circuit independence i
We should apply the new safety basis to all cable, not e
just the problem scope cable Therefore, further evaluation of walkdown findings was e
tabled in favor of developing a comprehensive solution l
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l Development of a New Safety Basis for Cable Separation I
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Why Do We Need a New Safety Basis?
Original design / license basis for cable separation lacks e
technical rigor Unclear technical basis for original design basis Evolving understanding of the elements important to safety e
for circuit independence Three elements of circuit independence e
Rote compliance with the original design / licensing bases in e
some cases will provide only minimal safety gain i
19
4 Original Criteria for Circuit independence Plant location to eliminate hazards Circuit overcurrent protection to prevent cable damage e
Physical barriers or separation to decouple hazards e
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l Features of the Original License Basis A barriered section of a cable tray is considered to be a e
separate raceway An armor jacket, flexible conduit, or metal barrier provides the required separation at tray ends, crossings, and transitions Instrument and Control circuits cannot self-ignite Separation in control panels provided by air separation, metal barrier, or flexible metal conduit Separation at control panel devices is dictated by the e
terminal arrangement NNS circuits are not separated from Class 1E circuits in panels or raceways Original design basis allows loss of redundancy as a direct e
result of a DBE Assumes that fire initiation is not possible due to low e
combustible loading 21
Later Enhancements to Address Fire Concerns Altemate Safe Shutdown System installed to compensate for e
insufficient' cable separation for fires in areas such as the Main Control Room, Cable Vault and Protected Cable Tray Room o
Significant attemate shutdown features Resolved open safe shutdown issues from 1978 fire e
protection SER e
Meets requirements of Appendix R Third path of safe shutdown equipment e
e Third diesel generator and power distribution center Lube oil leakage collection systems installed e
Key reason that Atherton issues from 1977/78 are not issues e
today 22 1
Cable Separation Safety Assessment Objectives Evaluate discrepancies identified by the field walkdown effort e
to identify the safety significance Identify the types of hazards that the cables may be subjected to in areas where separation discrepancies were identified identify measures which should be taken to eliminate the e
physical and electrical hazards posed to the cables because of the identified discrepancies Describe alternative methods and provide the technical Justification necessary to support the required FSAR changes and evaluation per the requirements of 10CFR50.59 23
i Hazards Evaluated e
Mechanistic hazards High energy line breaks Pipe whip Jet impingement Missiles and valve stem ejections Heavy loads impact by normal plant vehicle Electromagnetic interference (EMI)
Seismic events Lightning Strong winds and tornados Circuit faults / Breaker failures Excessive heating Metal splatter Electromagnetic interference (EMI)
Missiles Fires Floods 24
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Hazards Evaluated 1
Non-mechanistic hazards Maintenance and installation damage i
insulation damage
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Short circuit Accidental removal from service I
i Other physical damage i
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Protection from Hazards e
Mechanistic hazard protection Distance and plant location
' Circuit shielding Circuit overcurrent protection Physical barriers and separation l
Alternate shutdown (Safe shutdown only) e.
Non-mechanistic hazard protection Labeling and color coding i
Control of tools j
Training Circuit location Tray covers Work controls Access controis 26
l TE 172-97 FIGURE 3 IE CABLE t
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FIGURE 4 NNS CABLE i
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TE 172-97 FIGURE 2 CABLE FAULT POTENTIAL
IDENTIFICATION INSTRUMENT CONTROL POWER DAMAGE NO DAMAGE NO DAMAGE NOT WITH
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1E CABLES DAhiA
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PROTECT
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c e Significant Hazards to Cables Physical Damage from DBE (e.g. Pipe-Whip)
B Problem:
Original design basis allows loss of redundancy as a direct result of a DBE, which, in the face of less than adequate separation could challenge the independence of the redundant safety circuit.
Solution:
Provide improved circuit independence e
Prevent the hazard
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Or:
l Protect circuits required to mitigate the DBE from the effects of the DBE, including environmental qualification.
Class 1E circuits not required to mitigate the DBE and not protected from the effects of the DBE, including environmental consequences, are l
treated as potential hazards.
e Or, restore the original license basis separation IE a better l
safety improvement is not available.
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Significant Hazards to Cables d
Fault Hazards from Adjacent Cables (e.g. Cable ignition)
Eroblem:
Direct physical damage caused by a DBE in one area may propagate to other areas as a circuit fault, which, in the face of less than adequate circuit separation, could challenge the independence of the redundant circuit.
Solution:
j Provide improved circuit independence e
i Prevent the hazard i
e Or:
Circuits must be evaluated to identify and protect those circuits capable of producing fault currents large enough to cause cable damage NNS circuits with cable damage potential are assumed to fault coincident with a DBE.
NNS circuits which are not routed near Class 1E circuits are not a hazard.
Class 1E circuits not protected from the effects of a DBE are treated as a potential hazard.
Or, restore the original license basis separation IE a better safety improvement is not available.
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Significant Hazards to Cables Damage Caused by Maintenance Activity (e.g. Short Circuit) 3 l
Problem:
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Reduce or eliminate the maintenance induced interactions between redundant channels, which, in the face ofless than i
adequate circuit separation, could challenge the independence of the redundant circuit.
Solution:
Provide improved circuit independence o
Prevent the hazard Prohibit cable pulls through raceways which contain redundant channels of safety related cabling which is not physically separated while the functions served by the un-separated cable are required to be operable.
Prohibit the installation and removal of wires in control panels which contain redundant channels i
of safety related cabling which is not physically separated while the functions served by the un-separated cable are required to be operable.
Or, restore the original license basis separation IE a better o
safety improvement is not available.
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Significant Hazards to Cables Damage Caused by Maintenance Activity (e.g. Short Circuit) i Formalize additional good practices to further reduce the potential for common mode maintenance failures:
Clearly identify safety related circuits, raceways, and e
i devices implement strict access controls to the cable vault, e
cable chase, and interior of safety related control panels when the affected safety related circuits are required to be operable Establish a Foreign Material Exclusion (FME) process to provide tool and access controls in any area where cable tray covers have been removed, and when J
acce.ssing the Cable Chases or the Cable Vault Establish a Foreign Material Exclusion (FME) process e
to provide tool and access controls for the Main Control Board for on-line work and work controlled by the outage risk management program Add precautions to surveillance procedures which e
require test equipment terminations in the control panels Require the use of insulated tools when working in e
control panels include cable raceways in a periodic maintenance and e
inspection program to ensure that the level of protection provided by the raceways is not degraded.
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Eliminating Circuit Hazards 4
Physicallocation Relocate circuits and components e
j Provide physical damage restraint e
i Eliminate the hazard using procedures and j
administrative controls
.i Overcurrent protection l
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Provide double overcurrent circuit protection.
e Cable separation l
Relocate Class 1E circuits away from potential hazard circuits Provide metal barriers or physical separation e
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Safety Assessment implementation i
1)
Restore the original license basis separation IE a better i
safety improvement is not available.
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2)
Install required double overcurrent protection for Class 1E and NNS MCC,s, distribution panels, and heat trace distribution panels.
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Approximately 528 circuits affected:
.18 Class 1E control circuits j
360 Lighting, Utility, and Heat Trace circuits i
150 NNS MCC power circuits 1
j 3)
Class 1E circuits which are required to mitigate a DBE but are not protected from the physical damage caused by the DBE will be relocated or protected to achieve safety system j
independence l
CCW controls will be moved from the Turbine Building i
to the Protected Cable Tray Room.
i, Pipe restraints will be installed for the SG blowdown i
lines in the PAB pipe tunnel.
i Provide protection for the service water pump cable tray i
risers in the Turbine Building 33
Safety Assessment Implementation (Continued) 4)
NNS distribution buses exposed to DBE environment may require additional attention, e.g., automatically deenergized when a harsh environment is detected.
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5)
Existing NNS protective devices relied on for double i
protection will be tested prior to re-start, and a periodic testing program for these devices will be instituted.
6)
Scheduled raceways for safety related cables will be clearly l
identified in the field.
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7)
Safety related wires and devices in control panels will be color ceded to identify the train or channel association when of each Class 1E component.
l 8)
Additional maintenance controls discussed previously l
9)
Revise the FSAR to include the changes specified by this safety assessment.
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Conclusions Cable separation discrepancies are being dispositioned in an o
effective, comprehensive manner by:
Restoring originai license basis, or Implementing a safer altemative e
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insights from this effort:
Have resulted in better understanding of circuit e
independence elements important to safety
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Have been incorporated into the MY license basis e
e Overall, piant safety has been improved over the original license basis s
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